Diagnosis of the subgenus
Worker. Small ants (HL 1.00 - 1.70) with general characteristics of the genus. Anterior clypeal margin arcuate, majority of species with small notch or shallow emargination medially. Frontal carinae sinuate with laminate lobes; frontal triangle usually indistinct or visible only in certain illuminations and views. Eyes ranging from flattened to strongly protuberant. Preoccipital margin with a distinct ridge posteriorly and laterally in all but one species ( decora ), where it is suppressed by overlying cephalic sculpture. Mesosoma with dorsum showing all stages from fully marginate to completely immarginate. Pronotal humeri armed with spines, teeth or simply angular. Promesonotal suture present. Mesonotal and propodeal dorsa virtually fused. Metanotal groove completely lacking or only very weakly indicated by a hairline break in dorsal sculpture and / or by shallow incisions of lateral margins in species with marginate mesosoma. Propodeum terminating posteriorly in a pair of short teeth, tubercles or simply rounded, except in one species ( wilsoni ), where it is armed with long, mostly outwardly directed spines. Petiole scale-like; dorsal margin acute, usually entire, but occasionally with intercalary teeth or short spines, medially emarginate or unevenly jagged, laterally armed with short spines or teeth. In several species ( decora and its allies) petiole deeply transversely sculptured with dorsal margin more-or-less blunt. Base of first gastral segment usually concave medially, accomodating posterior face of petiole; dorsal margin of concavity acute or blunt and often raised above dorsum of segment; first gastral segment sometimes truncate or simply convex. Sculpture of head and body mostly consisting of regularly spaced striae that are either longitudinal or convoluted producing a characteristic “ geometrical ” appearance; gastral sculpture more modest, usually consisting of longitudinal striae; most distinct on sides of first gastral segment.
Queen. Very much like worker with usual characters identifying full sexuality, including three ocelli and complete thoracic structure with wings. Armament of pronotal humeri somewhat reduced, lateral petiolar spines distinctly shorter. Sculpture of head and body similar to that of worker, pattern of striation following structural characteristics of fully developed mesosoma.
Male. A single associated male is known for only one species (wardi) and as such has been omitted from this work. Hung (1967) studied the male genitalia of Polyrhachis and noted that they proved to be quite similar throughout the genus.
Distribution and biology. The known distribution of the subgenus ranges from the islands of eastern Indonesia (Aru, Misool), across the New Guinean mainland and adjacent islands (Umboi) to the Bismarck Archipelago, including New Britain and New Ireland. Little is known about their biology and nesting habits, however, a small colony of P. dohrni was collected by the author from a dry hollow twig on a living tree at the edge of lowland rainforest. The internal walls of the twig cavity were lined with a little silk. The only other record of a nest is of P. wardi , collected by Dr Phil Ward, also from a dry twig of a rainforest tree. The colonies of both species were rather small, with only a few workers (5 and 11 respectively, including 2 and 3 alate queens and a single male). If such a nesting pattern is the norm for other species of the subgenus, that might explain the general scarcity of Aulacomyrma material even in the best collections. This might also account for the fact that all previously described species were based on unique specimens. In spite of the exemplary cooperation of the listed institutions, this situation has only marginally improved in this revision with almost half the new species described from single specimens.
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